1. Field of the Invention
The instant disclosure relates to a method for removal of graphene layers; in particular, to a method for low-temperature and controllable layer-by-layer removal of graphene layers according to a pre-determined pattern.
2. Description of Related Art
Graphene, a single atomic thin material comprised of honeycomb carbon lattice, has attracted tremendous attention due to its exotic physical and mechanical properties compared with other known materials. Graphene possesses highest electrical conductivity and carrier mobility (>10,000 cm2/Vs) as a result of its Dirac energy spectrum at low energy. It demonstrates excellent optical transparency, and it also exhibits current density and thermal conductivity about 10 times higher than those of copper. The Young's modules of graphene is found to be 500 times greater than steel yet flexible. With the vast amount of excellent properties, graphene is an ideal candidate for transparent conducting electrodes required for applications such as touch screens, liquid crystal displays, organic photovoltaic cells, and organic light-emitting diodes, as well as the particularly popular organic light-emitting diodes (OLEDs).
Vast research in the field of graphene and graphene preparation has been done to pattern graphene. In an effort to further improve graphene removal processes, oxidation of graphene has been widely applied. Exposure of graphene layers in oxygen plasma is a typical method to remove or pattern graphene. Yet, the reaction is non-selective and hard to be controlled. Ozone is another reactive agent of choice for graphene oxidation. Ozone gas can be easily generated by ultraviolet excitation of molecular oxygen and used prevalently for disinfection and purification processes in which nitrogen, sulphur and carbon containing compounds are oxidized. In the field of graphene technology, ozone can be used to react with unsaturated carbon double bonds via a process known as ozonolysis. Oxidation process based on ozone generates only gaseous waste products, O2, CO, and CO2, which simplifies experimental procedures and waste treatment processes. The process can be conducted in vivo sealed chamber thus avoiding issues with transferring and exposure to the environment. Conventional research incorporates ozone treated graphene with post treatment of optical lithography and O2 plasma etching for the removal of graphene. However, analysis of ozone treated or optical lithography post-treated graphene shows the lack of selectivity in the specific number of graphene layers to be removed. Rather, either all the layers or portions of the layers are removed. Another conventional technique uses laser irradiation. To that end, high power lasers or femtosecond lasers are required. However, analysis of the laser irradiated graphene layers shows that all the layers tend to be completely removed due to overpowering laser which induces high temperature (>600° C.) at the targeted graphene areas. Lasers, such as high power-laser or high-energy-density laser (>8×10−4 mW/nm2) or femtosecond laser (>80 MHz), heats the graphene up to 600° C. or higher. However, the aforementioned lasers still cannot selectively remove the specific amount of graphene layers. The three aforementioned high power lasers also tend to damage the substrate thereunder. Thus, the laser irradiation method lacks efficiency, accuracy and selectivity in the specific number of graphene layers to be removed.
To address the above issues, the inventor strives via associated experience and research to present the instant disclosure, which can effectively improve the limitation described above.